I always find it interesting the way pilots interpret rules, Regs & advisories (CAAPS). It shows one thing that like a lot of rules & regs in any industry there is always a level of confusion or doubt.
Personally although I haven't joined a circuit as being described here for sometime but upwind is part of a std circuit anyway. You have crosswind, downwind base & final, final also being upwind as you may have gone around for various reasons so flying upwind say for another circuit is considered still being in the circuit for landing & you would not climb to above normal circuit height anyway (unless departing) so upwind is actually in the circuit.
To sum all that up you need to be at circuit height BEFORE joining upwind as you would for say joining downwind, how you do that is variable due some of the reasons already mentioned here.
Common sense is yr best defense:-)
Wmk2